1. Field of the Invention
This invention relates to an evaporated fuel processor of an internal combustion engine. More particularly, this invention relates to an evaporated fuel processor for preventing emission of an evaporated fuel generated in a fuel feed system of a vehicle into the open air, and to a fault diagnosing apparatus for such a processor.
2. Description of the Related Art
In a conventional internal combustion engine for a vehicle, a technology is known that temporarily adsorbs an evaporated fuel generated inside a fuel tank by use of an adsorbing member of a canister, introduces the evaporated fuel thus adsorbed from the canister into an intake passage in accordance with a driving condition and purges the evaporated fuel to prevent emission of the fuel into the open air.
As a prior art reference related with this technology, mention can be made of EP (European Patent) No. 0864741B1. This reference discloses a technology that introduces the evaporated fuel adsorbed to the canister into the intake passage of the internal combustion engine by use of an electric pump and purges it.
Since the prior art technology described above uses the electric pump, it can purge the evaporated fuel generated inside the fuel tank from the canister into the intake passage when the pressure difference between an intake pressure inside the intake passage and the pressure on the canister side is small, and also in the case of an inter-cylinder direct injection type engine in which the negative intake pressure cannot be acquired easily. However, since driving by means of a separate device such as an electric pump is necessary, the power loss rises to a certain extent, and this exerts an adverse influence on the fuel cost.
Recently, direct injection engines and other lean-burn engines that execute combustion using a mixture leaner than the stoichiometric air-fuel ratio are often used in order to improve the fuel cost. It is known that the leaner the air-fuel ratio in such engines, the smaller becomes the negative intake pressure. The evaporated fuel processor utilizes the negative intake pressure for delivering the evaporated fuel adsorbed by the canister into the intake pipe. Because the intake pipe negative pressure is small in the engines of the kind described above, however, the canister cannot be purged sufficiently, and the evaporated fuel remaining in the canister is likely to leak and to be emitted into the air.
To solve this problem, Japanese Unexamined Patent Publication (Kokai) No. 11-30158 describes a technology that arranges a purge pump inside a purge passage and delivers the evaporated fuel into the intake pipe. This reference discloses a motor driven-type purge pump that changes a purge amount to the intake pipe in accordance with the rotating speed of an electric motor, and a fuel driven-type purge pump that rotates a shaft by utilizing the flow of the fuel pressure-fed from the fuel tank into the injector and changes the purge amount into the intake pipe in accordance with the fuel flow.
However, the motor driven-type purge pump using the electric motor involves the problem of the increase of the fuel cost resulting from consumption of electric power. Though capable of solving the problem of the increase of the fuel cost, the fuel driven-type purge pump is not free from another problem that a part of the pressure generated by a fuel pump is lost because a part of the fuel branches from the fuel pipe and flows towards the purge pump during purge pump driving, and the fuel pressure of a fuel distribution pipe (delivery pipe) changes between purge pump driving and not driving, thereby exerting an influence on the fuel injection by the injector. Moreover, problems occur in that driving of the purge pump is limited during the driving condition where the fuel consumption amount is great, in order to secure the fuel amount to be sent to the delivery pipe, and that the pressure-feed capacity of the purge pump is restricted depending on the flow rate of the fuel (fuel consumption amount).
The present invention has been completed to solve the problems described above. It is, therefore, a first object of the present invention to provide an evaporated fuel processor of an internal combustion engine capable of reducing a power loss and securing a required purge flow rate in accordance with an operating condition of an internal combustion engine even when a pressure difference is small between an intake pressure inside an intake passage and a pressure in a canister.
It is a second object of the present invention to provide an evaporated fuel processor capable of restricting the influence on a fuel system and always exhibiting a stable purge capacity irrespective of an engine operating condition, and a fault diagnosing apparatus for the evaporated fuel processor.
It is a third object of the present invention to provide an evaporated fuel processor capable of compulsively desorbing an evaporated fuel from a fuel adsorbing layer by utilizing a purge pump without consuming electric power and without exerting an influence on the fuel injection by an injector.
In an evaporated fuel processor according to one aspect of the present invention, an evaporated fuel adsorbed by an adsorbing member in a canister is compulsively desorbed by driving of a purge pump and is introduced into an intake passage of an internal combustion engine. In this instance, an intake pulsation of an intake passage or an exhaust pulsation of an exhaust passage of the internal combustion engine is introduced into a driving chamber of the purge pump and a partition is moved, thereby varying a capacity of a purge chamber. Because the purge pump executes its pumping operation by utilizing the movement of the partition brought forth by the introduction of the intake pulsation of the intake passage or the exhaust pulsation of the exhaust passage of the internal combustion engine, the power loss can be reduced. Even when a pressure difference is small between the intake pressure inside the intake passage of the internal combustion engine and the pressure on the canister side, too, a required purge flow rate can be secured in accordance with the operating condition of the internal combustion engine.
In the evaporated fuel processor according to another aspect of the present invention, air forced into the canister by the driving by the purge pump compulsively desorbs the evaporated fuel adsorbed by the adsorbing member of the canister from the adsorbing member, and it is introduced into the intake passage of the internal combustion engine. In this instance, an intake pulsation of the intake passage or an exhaust pulsation of the exhaust passage of the internal combustion engine is introduced into a driving chamber of the purge pump with a predetermined valve operation, and the partition is moved. Consequently, the capacity of the pump chamber is varied. Because the purge pump executes its pumping operation by utilizing the movement of the partition brought forth by the introduction of the intake pulsation of the intake passage or the exhaust pulsation of the exhaust passage of the internal combustion engine, the power loss can be reduced. Even when a pressure difference is small between the intake pressure inside the intake passage of the internal combustion engine and the pressure on the canister side, too, a required purge flow rate can be secured in accordance with the operating condition of the internal combustion engine.
In the evaporated fuel processor according to another aspect of the present invention, there is disposed a purge pump that is driven by utilizing fuel pressure. In the purge pump, the fuel pressurized by a fuel pump is introduced and it reciprocates a movable member by the pressure of this fuel and compulsively purges the evaporated fuel adsorbed by the canister. Therefore, when the processor of this invention is employed for an engine having a low negative intake pressure (or not having a negative pressure), too, the evaporated fuel inside the canister is appropriately purged to the engine intake pipe. Since the fuel pressure is utilized to drive the purge pump in the present invention, the processor of the present invention does not invite a fluctuation of the fuel pressure due to leaking of the fuel or an adverse influence on the fuel system, unlike the conventional apparatus described in the prior art reference described above that utilizes the flow of the fuel to drive the purge pump. Since the fuel pressure (the fuel pressure by the fuel pump), as the driving source of the purge pump, is kept substantially constant irrespective of the operating condition of the engine, the purge pump can always be driven stably. As a result, the influences on the fuel system can be restricted, and the purge capacity can always be exhibited stably irrespective of the engine operating condition.
In the evaporated fuel processor according to still another aspect of the present invention, the purge air is introduced into a first chamber in the purge pump, the pressurized fuel is introduced into a second chamber by the fuel pump, and the movable member is reciprocated in accordance with the pressure of the fuel introduced into the second chamber. In this case, because the capacity of the first chamber changes with the reciprocation of the movable member, purge air is sucked into the first chamber and is thereafter delivered. Because the movable member partitions the first and second chambers under the sealed state in the present invention, leaking of the fuel pressurized by the fuel pump can be reduced to minimum. Consequently, the influences on fuel injection can be minimized.
In this specification, the purge air is a mixed gas of air introduced from the open air side in order to purge a canister and evaporated fuel purged by the canister (purged gas).
In a fault diagnosing apparatus for the evaporated fuel processor according to still another aspect of the present invention, a portion extending from the fuel tank to the intake pipe through the evaporated fuel passage is closed and this closed portion is then pressurized or evacuated by the purge pump. Any abnormality of the evaporated fuel processor is detected in this state, on the basis of the pressure change in the closed space. In this case, if any abnormality exists in the evaporated fuel processor inclusive of the canister and the purge pump, the evaporated fuel leaks out and can be detected as a pressure change in the closed space. Therefore, fault judgment can be easily practiced.
In the evaporated fuel processor according to still another aspect of the present invention, the negative intake pressure occurring in the intake pipe when the throttle of the engine is closed or opened, is utilized effectively, and this negative intake pressure is used as the power source for driving the purge pump. The purge pump, driven by the negative intake pressure as the power source without consuming electric power and without exerting adverse influences on fuel injection of the injector can compulsively desorb the evaporated fuel from the fuel adsorbing layer, and can deliver the evaporated fuel so desorbed from the fuel adsorbing layer into the intake pipe through the purge passage.
The present invention may be more fully understood from the description of preferred embodiments thereof, as set forth below, together with the accompanying drawings.